Navigational radar reflector systems



Jan. 22, 1957 s. CSBERG NAVIGATIONAL RADAR REFLECTOR SYSTEMS Original Filed April 13. 1951 \izg 3 Sheets-Sheet 1 IN VENTOR .SVE/V 0am,

BY WBQ ATTORNEY all Few

Jan. 22, 1957 Original Filed April 13. 195] S. QBERG NAVIGATIONAL RADAR REFLECTOR SYSTEMS 3 Sheets-Sheet 2 l N VEN TOR 6 VE/V 055;?6,

ATTORN E Y Original Filed April 13, 1951 Jan. 22, 1957 s. OBERG 2,779,019

NAVIGATIONAL RADAR REFLECTOR SYSTEMS 3 Sheets-Sheet 3 \S VEW 65596,

ATTORNEY United States Patent NAVIGATIONAL RADAR REFLECTOR SYSTEMS Sven fiberg, Stockholm, Sweden, assignor to Svenska Aktiebolaget Gasaccumulator, Stockholm-Lidingo, Sweden, a company Original application April 13, 1951, Serial No. 220,757.

Divided and this application October 11, 1954, Serial No. 461,585 i 3 Claims. (Cl. 343-18) This application is a division of my co-pending application Serial No. 220,757 filed April 13, 1951.

This invention relates to navigation devices and more particularly to devices by which the position of objects can be located through the use of radar.

According to the broad principle of radar, a pulsed signal of a very high frequency is transmitted by a rotating antenna so as to scan the area adjacent the transmitter. Objects in the area will reflect the signal back to the transmitterwto give an indication of the presence of the object. The reflected beam is directed to a cathode ray oscilloscope whose electron beam is constantly sweeping the scope in synchronism with the movement of the antenna. The intensity of the electron beam is influenced by the reflected radar wave, so that, for example, the electron beam is fully. or partly suppressed when no reflected beam is received but obtains full intensity when a reflected beam is received.

Thus, the oscilloscope will indicate the position of the objects causing the reflection of the input of the radar beam.

The angular position on the screen will be determined by the angular position of the transmitter antenna. The indication on the screen of the distance of the object from the transmitter will be dependent upon the time required for the signal to be transmitted to the object and then reflected back to the transmitter.

The principles outlined above havebeen utilized as navigational aids for airplanes, ships and the like. One arrangement proposed involves the useof so-called radar reflectors. Such a reflector in its simplest form may consist of a metal disk forreflecting a radar beam as de scribed above. As a rule the disk is not completely satisfactory because only in exceptional cases will it reflect a beam back to the transmitter. A better solution of the reflector problem is obtained by arranging two reflector plates at an angle to each other, and one of the best solutions consists in the arrangement of three reflector platesfbuilt together as a pyramid. These reflectors will iunction in the same way as the total reflecting pyramid known in the optical art.

These reflector arrangements, however, have the disadvantage that they will cause only a single point to be received on the oscilloscope screen and the single point is diflicult to separate and distinguish from other points inadvertently received on the screen. Nor has it been possible with such known arrangements for the operator to identify the particular reflector being observed.

It is the object of the present invention to provide a reflector arrangement by which the operator can easily distinguish the reflector being observed from random spots on the radar screen, and further to provide a code by which each reflector can be identified by the operator. This and other objects are accomplished by a reflector system which operates entirely on signals reflected from objects constructed and arranged according to-the present invention.

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.. Fig. 3 is a diagrammatic view of a reflector'arrange- V ment illustrating the principle of the invention. Figs. 4a and 4b are diagrammatic perspective views of reflectors which may be used in the arrangement of Fig. 3.

Fig. 5 is a diagrammatic view of amodification' of the arrangement of Fig. 3. a p i Fig. 6 is a diagrammatic view of a further modification of the arrangement of Fig. 3. t l

Figs. 7 and 8 are diagrammatic views illustrating the reflector to be used in the system of Fig. 6, and

Figs. 9-12 are diagrammatic views of still further modifications of the arrangement of Fig. 3. i i

Fig. 1 shows a known radar'reflector which operates according to the pyramidic principle. The reflector is constructed from three reflector screens 11, 12 and 13 connected together as sides of a pyramid with the angular relationship of the sides so designed that an input signal Wave will always be reflected backwards in its own input direction. The angular relationships are known from the optical total reflecting pyramid. Thus, for in stance, the beam 10 is first reflected against the side 11, thereafter against side 12 and finally against side 13. Thereafter, the beam returns in its own initial direction as beam 14.

Fig. 2 shows an arrangement consisting in eight re flectors of the type shown in Fig. I mounted together to a spherical body. This arrangement has proved to be very eflective even for marine navigation purposes in which the two vertically directed pyramid openings are not effective.

In the arrangement shown in Figs. 1 and 2, the input wave will be reflected back in the direction from which it originated regardless of its angle of approach to the reflector. When the wave comes inat an angle to all three sides, the reflection will take place from all three surfaces. On the other hand, if the input beam is parallel to one of the sides, only two reflections, from the remaining two sides, will benecessary to return the beam back to its sourcer Therefore, .if it is known in advance that the input signal will always be in the horizontaldirection, it will be necessary to construct the reflector of only two screens having their planes extending in the vertical direction. The invention will be described in connection with such a reflector although it is to be understood that the invention may be used equally well with the total reflecting pyramid. In order to simplify the description still further, the disclosure will deal primarily with the navigation of ships, although it is further to be understood that the invention may be applied equally well to the navigation of aircraft and the like.

In all of the embodiments shown and described, it will be assumed that the reflector is mounted on solid ground so that it may have a predetermined fixed position and that the radar beam from the vessel strikes the reflector horizontally.- If these conditions cannot be satisfied, one skilled in the artcan modify the arrangement to suit the particular need.

The principle of the-invention is illustrated in Fig. 3. Tworeflectors 15 and 16 are placed in fixed positions on two low rocks in an island group'for example. The reflector 15 is a simple angular reflector consisting of two screens of the type referred to above. The reflector 16 is a combination of two such angular reflectors one directed toward reflector 15 and the other directed away AVA , The operation of the wide angle reflector 40 can be explained by reference to the schematic diagram in Fig. 7. The reflector is constructed to two reflecting screens 42 and 43. If an input beam has the direction 44, this will first be reflected against the screen 42 and then against screen 43, but because of the wide angle will not be returned in the direction from which is originated. Rather, it will take a direction differing from the input direction by the angle (1:.

If the opening angle of the wide angle reflector is 6, it is obvious that the relation between the angle and the angle 6 will be:

In the system according to Fig. 6, the right angle reflector 41 should therefore be placed in the horizontal plane in a direction from the reflectors 38, 39, which is separated from the direction of the input beam by an amount of 1S0-. If the reflector 41 is positioned as described above, then the input beam will be reflected from the wide angle reflector 40 to the reflector 41 and then back toward the reflector 39 or 40 along the original ath.

p An application of the system described with respect to Fig. 3 is shown in Fig. 9. It is possible by the use of reflector pairs of differing lengths between reflectors to provide a code-like division of the virtual images. In the system of Fig. 9, there are two pairs of normally cooperating reflectors, namely, the reflector pair 63-64 and the reflector pair 6566. The distance between the reflector 63-64 is different from the distance between reflectors 65-66. In the-example shown in Fig. 9, the distance between reflector pair 6364 is exactly twothirds of the distance between reflector pair 6566.

The reflectors may be provided one over the other, but in practice it is often more suitable to mount the reflector pairs at the same level as indicated in the drawing.

The connection lines between two reflectors in each pair are parallel to each other as well as to an indicated bearing line 67 in which a vessel 68 is assumed to be situated.

Further, the distance between the two connection lines should be so small that no dissolution of the virtual images will take place. The distance, however, should be so great that no cross-reflection takes place such as reflection in the following sequence: 6863-6465 68- If these conditions are satisfied, the vessel at 68 will see a pattern created as follows:

The reflectors 63 and 64 will create a band of dots containing the dot 69 indicated by direct reflection and thereafter the dots 7078. The reflectors 65 and 66 simultaneously create an amplification of dot 69, a free dot 76, an amplification of the dot 72, a free dot 80, an amplification of the dot 75, a free dot 81, an amplification of the dot 78 and so on. The vessel at 68 will therefore see'in its radar scope a code band of dots containing alternatively one bright dot, for example, 69, 72, 75 and 78, and three intermediate dots of lesser brilliance indicated, for example, by the group 70, 79 and 71, or the group 73, 80 and 74, or the group 76, 81 and 77.

The field allowed for navigation is in the present case limited by the connection lines between the reflectors 63 and 66 and the reflectors 64 and 65, which form the angles a and [3 respectively with the bearing line 67. The limitation lines in the drawing are indicated by 82 and 83 respectively. These limitation lines are intended to limit the navigation range with respect to a couple of shallows 84 and 85 present in the navigational water.

If a vessel should get as far as the limitation line 82 as shown by vessel 86, its radar beam will be reflected by the reflectors 63 and 66 without any cross reflection with the reflectors 64 and 65. The consequence of this reflection will be a simple band of dots 69, 87 and 88 i 6 to 92' with equal distances between the dots. The presence on the radar scope of such evenly spaced dots will warn the pilot that he should steer closer to the allowed navigational angle.

If the pilot should approach the other limitation line 83 as indicated by vessel 93, he will also see evenly spaced dots 69, 94 to 101. The distance between the dots is different in the two limitation lines 82 and 83 so that the pilot can identify the particular limitation line he is on and can thereby determine whether to yaw portor starboard.

The drawing has been exaggerated in its scale in order to present a clear picture. In practice, however, the angles a and ,8 should be limited to the order of magnitude of 1 to 5.

82 or 83 will obtain some cross reflections on the radar scope. Thus, the vessel will in its scope see a band of all the dots which are spaced at distance equal to the distance between the reflectors 63 and 64 on one side and the reflector 65 and 66 on the other side, as is also evident from Fig. 9.

It is possible to modify this system of Fig. 9 by the use of side reflectors in a manner which has already been described in connection with Fig. 6. Fig. 10 shows such a modification of the system of Fig. 9 in which the different reflectors are provided with the same reference numerals as in Fig. 9 with the addition of a prime. It should be evident from the description of Fig. 9 how this system according to Fig. 10 functions in general.

In Fig. 10, the side reflectors are both disposed on the same side of the allowed navigational angle. The system would not be changed in any major respect if the reflectors 64 and 66 were located each on one side of the allowed navigational channel. Such a modified system is shown in Fig. ll, the same reference numerals being used with double primes being added.

The systems according to Figs. 10 and 11 have an advantage over the system according to Fig. 9. In order to provide a code, which is the function of these systems, it is necessary that the distance between reflector pairs be in a fixed relationship, such as 2:3 as in the chosen example. In the system of Fig. 10, the fixed relation between the distances between pairs influences the magnitude of the angles a and 5. As long as these angles are small, one may assume with good approximation that the angles also have the relationship to each other of 2:3.

However, it would be advantageous if the navigation space was equally great on each side of the given bearing line. This may be obtained'by adjustment of the reflector angles for the wide angle reflectors of the systems of Figs. 10 and 11.

A code-like grouping ofvirtual images similar to those discussed in connection with Figs. 9 to 11 can also be obtained with the system of Fig. 12. In this system, there are two complete groups of reflectors of the type shown in Fig. 6. These are spaced a comparatively short distance from each other in the direction of the input beam. It is immediately apparent from the drawing that the signals will be repeated with a distance which is determined by the distance between the reflectors 103 and 104 or between the reflectors 105 and 106; The radar scope will show double dots, the spacing of the double dots being determined by the distance between the reflectors 103 and 105.

Other combinations of the above described reflector groupings will become apparent to those skilled in the art so that it will be seen how further code signals can be arranged for navigational purposes.

In a general manner, while there has been disclosed in the above description, what is deemed to be the most efficient and practical embodiment of my invention, it should be well understood that the invention is not limited to such embodiment as there might be changes made in If the angles are in this range, a vessel in the intermediate zone between bearing line 67 and lines f: the scope ofi'tlre} accomga'nyi'ng sy 't' m intended for radar purposes, comaggr gate of reflectors including a first q 'it ihg' 'a'signalbearn and reflectinga first of s 3 li mi, back", to it's, transmitter, a second g a second portion, of saidv beajn aidfirst' 'refl'e'cfor, said"reflectoi's having cooperatces disposed in beam. aligned relationreflected liack'andforth, the. remaim I u e 'nd', portion'liein-gdirectedb'a'ck V ",the secohd ag reg te of reflectorslike te "offr'eflectorsi' and cooperating with o, indicatefa complicated radar piccondr'eflectors in said. first aggregate 1 shin'ggport'ions of'said second portion eendieemeate; rr r t for ifr n th f peated efleptipn' m e tee e tea- 3. M sre ninef n eat "2; A reflector syst'er'n according wto clairn l, in which the aggregatesare placed so in relation to each other that within" a 'giyen range no cross reflection between. the aggregates willlemanate whereas, however, when deviat-- i'ng to one or the other or both sides from this rangethere will be cross reflection, the code-like reflection. grouping thereby beingchanged. V

3. A reflector system according to claim 1, in which in each reflector aggregate said first reflector includes a wide angle neflectqrgand sai seco e te is; lo ate 15 at the side of said first reflector tocooperate with said Wide angle reflector to cause said back and forth reflection of. said diminishingeportions.

No references cited.

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